Fiber optic ribbons are comprised of an array of multiple optical fibers grouped together in any size in a ribbon and secured to a substrate. Typically, the ribbon is about 0.01 to 0.03 inches thick. If one or more surfaces of the ribbon are marred or abraded and a light source is applied to one end of the marred ribbon, light will be emitted from the marred area. Accordingly, efforts have been made to create a specific illumination pattern which can be effectively used to backlight a variety of displays. For example, stamping the ribbon with a roughened plate was used to provide marring of fiber optic ribbons. In this approach, a ribbon would be placed on a cushion and a stamp having a covering, such as emery paper, would be pressed against the ribbon to deform or mar the surface. To increase the amount of surface marring along the ribbon, the cushion was placed on a plate having a particular profile, such as an uprising surface or a symmetrical curved plate. For further details, see U.S. Pat. No. 4,929,169 to Fujigaki et al. entitled "Working Equipment For Roughing The Side of Optical Fiber".
The stamping method can only mar a fixed length of ribbon at a time limited by the size of the stamp. Different sized stamps thus are required to mar different length of ribbons. As such, different forces need to be applied in order to achieve the same desired pressure profile against the cushion and plate. These cumbersome limitations severely restrict the stamping method to produce a desired marring pattern only along a short portion of the ribbon. In addition, the plates on the apparatus need to be changed, a cumbersome and time-consuming procedure, whenever a different marring size is desired. Presently, different patterns are not possible.
An improved method and apparatus for marring the surface of a fiber optic ribbon over the stamping method has been disclosed in pending U.S. application Ser. No. 07/785,130 entitled "Method And Apparatus For Marring Fiber Optic Ribbons", (hereinafter known as the nip method) also assigned to the assignee of the present invention, Poly-Optical Products, Inc., reference to which is being hereby incorporated by reference.
In this nip method, the fiber optic ribbon is being fed between a pair of rotating rollers. One of the roller is coated with an abrasive. The second roller may be hard, have a deformable cover or also have an abrasive coating. Alternatively, one or both rollers may be serrated to produce a ripple pattern in the fiber optic ribbon. This nip method using an abrasive coating on the roller(s) for marring the surface of a fiber optic ribbon has a number of advantages over the earlier stamping method.
For example, because surface marring occurs as the fiber optic ribbon is fed through the gap between the rollers, less force is required to mar the fiber optic ribbon than in the earlier stamping method. The nip or contact pressure line between the rollers is easier to control and accurately maintain than pressure developed across a stamping plate. A further advantage of the nip apparatus and method is that various marring patterns may be created on the ribbon surface by adjusting the speed of the ribbon through the nip and/or altering the pressure in the nip as the ribbon moves therethrough and/or creating a pressure differential along the nip or contact pressure line between the rollers. In other words, most any illumination profile along the surface of the ribbon is possible. Despite its improvements over the earlier stamping method, the nip method is limited. The nip method is limited because the light output is limited by the uniform abrasive coating on the roller(s) rendering it extremely difficult to provide high light output to specific areas as is required to back light a company logo design display. In addition, the nip method is cumbersome because the gap in the nip needs to be adjusted during processing to achieve a gradual differentiation of surface marring along the ribbon. Moreover, the nip method often introduces a "seam" that is transferred onto the ribbon from the roller when the abrasive coating on the roller(s) is used. This seam causes a break in the pattern being marred onto the ribbon and leads to flaws in back lighting of the display.
Therefore, a need has developed for a system and method that permit processing a specific design onto a fiber optic ribbon having different lengths of abrasion or that require different display patterns without interrupting operation of the system to substitute suitable parts. It is also desirable that such a system be capable of gradually and accurately altering the pressure profile applied to the ribbon, again without interrupting operation of the system.